UVGI in Ventilation Ducts & Re-circulating Room Air Disinfection Units

Transcription

1 UVGI in Ventilation Ducts & Re-circulating Room Air Disinfection Units Part 3: Recirculation UVGI Systems, Zonal Protection Factor, In-place testing Protocols Dr. Wladyslaw Jan Kowalski, PE, Immune Building Systems, Inc.

2 Stand Alone Recirculation UV Systems Vary widely in performance, shape, and size Often very low exposure times, very high intensity No reciprocity for short exposure times Increasing irradiance does not make up difference below 0.25 secs Microbes may have nonlinear response (shoulders) Performance can be defined by URV and CADR CADR = Removal Efficiency x Airflow For many systems Removal Efficiency > 95% and CADR is approximately same as Airflow CADR will define applicable Floor Area or Zone Volume Zonal Protection Factor (ZPF) can be used as rating basis Only known Guideline ANSI/AHAM (2002) AC Standard Method for Measuring Performance of Portable Household Electric Air Cleaner ARI (Air Conditioning and Refrigeration Institute is also developing test methods and standards

3 Recirculation UVGI Systems

4 UV Recirculation Unit

5 EPA Test Results for Unitary System

6 Air Treatment & Zone or Building Interaction Aerobiological Performance of air cleaning systems is determined by the interaction of the building and the air treatment system Combined performance can be modeled minute-by-minute Multizone (Building) Modeling can be performed with CONTAM (NIST software) Performance can be interpreted with a ZPF or BPF

7 Zonal Protection Factor Defined as the Percent of Occupants who do not become infected Can be predicted analytically on the basis of inhaled dose over 8 hours Same as Building Protection Factor (BPF) for Multizone Buildings First calculate airborne concentrations over time Sum inhaled dose over 8 hours Estimate infections from ID50 for target microbe (i.e. TB, influenza) Under Baseline conditions, no air cleaning, 99% infections are assumed, and release rate can be estimated (The release rate produces 99% infections after 8 hours) Under Air Cleaning, same release rate, infection % will decrease Infection % with air cleaning is the ZPF Concentration, cfu/m Steady S Transient Infections, % Steady State Transient Time, hours Time, hours

8 ZPF/BPF Calculator Download Building Protection Factor - Simplified Steady State Model Input Data Parameter Value Units Notes Enter Floor Area 4000 ft 2 FA Ceiling Height (adjust to match building volume) 8 ft Optional Enter System Airflow 3200 cfm Qt Enter Normal Operating Removal Efficiency 0.7 fractional MPP Enter Maximum Removal Efficiency 0.99 fractional MPP Enter Normal Operating Outside Air 15.0 % Recommended Outside Air (20 cfm per person) 13 % Enter Building Type (1-6) 4 see Table 1 Btype Building Type Residential, Apartment Area per Occupant 200 ft 2 per person Occupants 20 Building Volume ft 3 Baseline Outside Air 15 % Baseline Outside Air Exchange Rate 0.9 ACH Total Air Exchange Rate 6.00 ACH Release Rate 9.45 cfu/min NOTE: MPP = Most Penetrating Particle (use for filter/uvgi removal rates) Simplified Steady State Results Condition OA CADR Css 8h Dose Infections BPF m 3 /min m 3 /min cfu/m 3 cfu % % Baseline Normal Operating Maximum Air Cleaning NOTE: CADR = Clean Air Delivery Rate (Total Airflow x Removal Efficiency) Transient Results Condition OA CADR 8h Conc. 8h Dose Infections BPF m 3 /min m 3 /min cfu/m 3 cfu % % Baseline Normal Operating Maximum Air Cleaning Net Error of Simplified Model 0.59 % Prototype BPF Calculator, written by W.J. Kowalski, Penn State Indoor Environment Center, version 2005-A-5. Infections, % Steady State Transient Time, hours Figure 1: Steady State vs. Transient Infections -- Baseline Condition Infections, % 18 Steady State 16 Transient Time, hours Figure 2: Steady State vs. Transient Infections -- Normal Condition

9 Typical Unitary UV System

10 Installation Requirements UL Listed Components UL Cabling Safety Switches Door Interlocks Warning Signs Reflective Materials Breakage

11 In-Place Testing Protocols UV Output Measurements No protocols, Check for UV leakage only Cooling Coils: measure mean irradiance on surface Measure Reduction of Airborne Microbes Upstream vs. Downstream Before vs. After (wait ~2 weeks minimum) Ambient Fungi or Bacteria Human Bacteria (occupied) Measure Reduction of Surface Microbes Before vs. After (wait 2 days minimum)